The price of gold has nearly doubled in the past two years, posing new economic challenges for industrial coating processes. Against this backdrop, solutions for material efficiency and targeted control of coating thicknesses are becoming increasingly important. With its Auruna 526 and Auruna 527 hard gold electrolytes, Umicore Metal Deposition Solutions (MDS) offers processes for small-part mass coating that are designed to ensure uniform gold deposition.
Uniform deposition at varying current densities
The weakly acidic gold-cobalt (Auruna 526) and gold-nickel electrolytes (Auruna 527) were developed for use in barrel plating and vibration coating systems. These processes are characterized by widely varying current density conditions for individual components. The aim of the electrolytes is to deposit a uniformly distributed gold layer of a defined minimum thickness even under these conditions.
Especially with complex geometries such as plug contacts, contact sockets, or sleeves, it is often difficult to achieve a homogeneous layer distribution with conventional electrolytes. Auruna 526 and Auruna 527 enable a more uniform deposition both on exposed areas and in recesses or cavities.
Reduced gold consumption thanks to balanced layer profile
The two hard gold electrolytes are characterized by a balanced ratio of deposition rates. While increased deposition occurs at low current densities, the deposition rate is significantly reduced at high current densities. This prevents overcoating, which often occurs with standard electrolytes. In comparison, drum and vibration coatings of bulk materials in particular show more uniform layer thicknesses and a significant reduction in the so-called dog bone effect.
These properties make it possible to maintain the required minimum coating thickness at defined measuring points without using additional gold. This saves material and costs, especially for internal measuring points on sleeves and bushings.
Properties of the deposited hard gold layers
The hard gold layers deposited with Auruna 526 and Auruna 527 are abrasion-resistant and meet the requirements for corrosion protection and low contact resistance. In internal test series, contact transition resistances of 3.33 mOhm for Auruna 526 and 3.26 mOhm for Auruna 527 were determined at a test force of 50 cN. The layers comply with ASTM standard B 488-01, Type I, Code C, making them suitable for demanding applications such as defense technology. This is based on a fineness of around 99.8 percent and a hardness of around 150 HV.
According to Umicore MDS, demand for these hard gold electrolytes is increasing, particularly due to the current development of precious metal prices. Another aspect is their easy integration into existing coating lines. The electrolytes have a wide working window, stable long-term behavior, and comparatively uncomplicated process control.